The duplex composite member of the present invention may have desirable surface properties such as resistance to chemical attack and/or mechanical shock and vibration, making it especially well suited for applications in incandescent lamps, metal halide discharge lamps, and/or halogen incandescent lamps.
Electrode and/or filament failure due to mechanical shock and/or chemical attack is a recognized problem in the lighting industry. For example, U.S. Pat. No. 4,413,205 describes in detail how the tungsten conductors to the coiled filament of a halogen incandescent lamp are locally pitted and chemically attacked by bromine in such a manner that they break and the lamp fails.
The 4,413,205 patent suggests one method for reducing this chemical attack problem, namely, modifying the conductor material to a tungsten rhenium (Re) alloy containing at least 0.1% Re.
Similarly, it is known that filament and/or electrode failure due to chemical attack can also occur in metal halide high intensity discharge (HID) lamps, especially where reactive halogens, including bromine, chlorine, and iodine have been used. See, for example J. F. Waymouth, "Electric Discharge Lamps" pg. 210, (1971).
The chemical attack of thoriated tungsten electrode rods thus constitutes a recognized obstacle in the application of the reactive halogens in metal halide discharge lamps.
Although such changes in electrode composition as those described in the 4,413,205 patent may overcome the problem of electrode failure due to chemical attack, such alloys suffer from two major shortcomings:
(a) they do not possess the necessary emissive characteristics of the W - (usually 1-2%) ThO.sub.2 materials typically used for electrodes and
(b) they introduce excessive Re emission into the light emitting plasma discharge of metal halide lamps.
The present invention is directed to an alternate solution to the problems of chemical attack and/or mechanical shock of electrodes and/or filaments, which does not suffer the disadvantages discussed above.